The present invention relates to a vibration damper for damping vibration of a drum brake in a positive manner, thus suppressing squeals of the drum brake during braking.
Most widely used means for reducing squeals of disc and drum brakes are mechanical vibration dampers for damping vibrations by binding the brake shoes or the friction pads with resilient members or moving the portions pressed against each other. More recent dampers include one that utilizes feedback control, as disclosed in unexamined Japanese patent publication 4-54325.
The damper disclosed in this publication, which is shown in FIG. 8, comprises a vibration detection sensor 115 provided on the back of a friction pad 112 for detecting the vibration of the pad, and a vibration actuator 116 provided parallel to the sensor 115 for suppressing the vibration of the disc 110, thereby reducing squeals of the brake.
In this conventional arrangement, the vibration of a friction pad, which is one of vibration sources, is detected and vibration force is applied to the pad. But since the main vibration source is the disc, it is difficult to efficiently damp brake vibrations.
In the above prior art, since the vibration detector detects the vibration of the friction member to which the vibration force is applied from the vibrator, the detector inevitably detects the vibration component applied from the vibrator, besides the vibration of the disc itself. Since it is impossible to detect only the vibration of the disc, detection accuracy is low. Since the vibrator applies vibration force based on the detection signal from the detector, it is difficult to efficiently reduce the vibration of the disc.
An object of the present invention is to provide a drum brake vibration damper which can eliminate the above-described undesirable vibration component from being picked up and can produce more proper vibration signal.